Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005     

Removal of phosphate anions from aqueous solutions using polypyrrole‐coated sawdust as a novel sorbent

This work was focused on the removal of phosphate ions using polypyrrole‐coated sawdust as a novel cost‐effective sorbent. The phosphate uptake followed the Langmuir sorption isotherm, and the sorption capacity at 20, 35, and 50°C was found to be 17.33, 23.41, and 30.39 mg/g, respectively; this indicated favorable sorption at higher temperatures. The kinetic uptake data were modeled with the Lagergren equation, first‐order and second‐order kinetic models, and the simple Elovich model. The results indicated that the Lagergren model best described the uptake data. The intraparticle diffusion coefficient, as determined for 250–211‐ and 630–600‐μm sorbent particles at 20°C, was found to be 287.3 × 10^?2 and 228.3 × 10^?2 mg g^?1 min^?1, respectively. The intraparticle diffusion was also confirmed with the Bangham equation. The sorption mean free energy, calculated with the Dubinin–Radushkevich equation, was found to be 10.98 kJ/mol, thus confirming an ion‐exchange regulated sorption process. The positive value of the enthalpy change (i.e., 4.23 kJ/mol) confirmed the endothermic nature of the sorption process. The negative values of the change in the standard free energy were indicative of the spontaneous nature of the sorption process. Finally, the activation energy of the sorption process for 250–212‐μm particles, determined with the Arrhenius equation, was found to be 41.68 J/mol. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of high‐molecular‐weight poly(vinyl alcohol) with high yield by solution polymerization of vinyl acetate in methanol using 4,4′‐azobis(4‐cyanovaleric acid)

Vinyl acetate (VAc) was solution‐polymerized at 40°C and 50°C using 4,4′‐azobis(4‐cyanovaleric acid) (ACVA) as an initiator and methanol as a solvent, and effects of polymerization temperature and initiator concentration were investigated in terms of conversion of VAc into poly (vinyl acetate) (PVAc), degree of branching (DB) for acetyl group of PVAc, and molecular weights of PVAc and resulting poly(vinyl alcohol) (PVA) obtained by saponifying with sodium hydroxide. Slower polymerization rate by adopting ACVA and lower viscosity by methanol proved to be efficient in obtaining linear high‐molecular‐weight (HMW) PVAc with high conversion and HMW PVA. PVA having maximum number–average degree of polymerization (P_n) of 4300 could be prepared by the saponification of PVAc having maximum P_n of 7900 polymerized using ACVA concentration of 2 × 10^?5 mol/mol of VAc at 40°C. Moreover, low DB of below 1 could be obtained in ACVA system, nevertheless of general polymerization temperatures of 40°C and 50°C. This suggests an easy way for producing HMW PVA with high yield by conventional solution polymerization without using special methods such as low‐temperature cooling or irradiation. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 4831–4834, 2006     

Rheokinetic of a gelled resol resin curing by dynamic‐temperature rheometry based on rectangular torsion strain

The rheological behavior of a phenolic resol resin during its curing process was studied through a rheological dynamic‐temperature analysis. Two heating ramps from 0 to 120°C (1°C/min) and from 0 to 150°C (5°C/min) were performed. The resin's complex viscosity data were obtained by applying a rectangular torsion strain. The overall change of complex viscosity with temperature was due to a combination of thermal softening, described by the Andrade equation, and the resin crosslinking process. The four‐ and six‐parameter Arrhenius rheokinetic model was applied to the profiles obtained for the resin's complex viscosity, and the viscous flow and activation energies of curing kinetics were established. Two calculation methods are proposed to obtain the flow and curing parameters of the material. The six‐parameter Arrhenius model was more suitable for predicting changes in the resin's complex viscosity, obtaining an activation energy of ～ 38.0 kJ/mol for the resol resin curing process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of a star‐shaped polystyrene‐b‐poly(ethylene‐co‐propylene) block copolymer as a viscosity index improver of lubricant

A saturated star‐shaped polystyrene‐b‐poly(ethylene‐co‐propylene) block copolymer, (SEP)_star, was synthesized for use as a viscosity index improver in lubricants. Polystyrene‐b‐polyisoprene arms were first made anionically, followed by a linking reaction at the optimum temperature of 60°C with divinylbenzene. The resulting star‐shaped (SI)_star was hydrogenated to eliminate the double bonds on the polyisoprene segment, thus forming the star‐shaped (SEP)_star. The number of arms on each molecule increased with an increase in the mol ratio of divinylbenzene to n‐butyllithium. Increasing the arm length adversely affected the linking efficiency but caused a slight increase in the degree of branching. The T_g of the poly(ethylene‐co‐propylene) block was 13°C higher than that of the original polyisoprene block. Compared with (SI)_star, (SEP)_star has a thermal decomposition temperature 50°C higher but independent of the arm length or the degree of branching. Viscosity measurements for (SEP)_star revealed that intrinsic viscosity depends only on the arm length, but not on the degree of branching. Adding 1 wt % of (SEP)_star markedly increased the viscosity index of a HN base oil. With a fixed arm length, a (SEP)_star having a higher degree of branching increased the viscosity index more than that having a lower degree of branching. On the other hand, the viscosity index increased with an increase in the arm length when the degree of branching was fixed. The addition of 1wt % of (SEP)_star increased the vioscosity index up to a number between 111 and 166, with the exact number depending upon its arm length and degree of branching. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1838–1846, 2001     

Properties of isocyanate‐reactive waterborne polyurethane adhesives: Effect of cure reaction with various polyol and chain extender content

Three series of isocyanate‐reactive waterborne polyurethane adhesives were prepared with various contents of chain extender (4.25/8.25/12.50 mol %) and polyol (20.75/16.75/12.50 mol %). Each series had a fixed amount of excess (residual) NCO group (0.50–2.00 mol %). FTIR and ¹H‐NMR spectroscopy identified the formation of urea crosslink structure mainly above 80°C of various cure temperatures (20–120°C) with excess diisocyanate. The molecular weight, tensile strength, Young's modulus, and adhesive strength depend on excess NCO content and cure temperature and also varied with polyol and chain extender content. The optimum cure temperature was 100°C for all the samples. The tensile strength, Young's modulus, and adhesive strength increased with increasing cure temperature above 60°C up to the optimum temperature) (100°C) and then almost leveled off. Among all the samples, the maximum values of tensile strength, Young's modulus, and adhesive strength were found with 63.22 wt % polyol, 0.93 wt % chain extender, and 1.50 mol % excess (residual) NCO content at 100°C optimum cure temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Curing kinetics and viscosity change of a two‐part epoxy resin during mold filling in resin‐transfer molding process

The curing kinetics and the resulting viscosity change of a two‐part epoxy/amine resin during the mold‐filling process of resin‐transfer molding (RTM) of composites was investigated. The curing kinetics of the epoxy/amine resin was analyzed in both the dynamic and the isothermal modes with differential scanning calorimetry (DSC). The dynamic viscosity of the resin at the same temperature as in the mold‐filling process was measured. The curing kinetics of the resin was described by a modified Kamal kinetic model, accounting for the autocatalytic and the diffusion‐control effect. An empirical model correlated the resin viscosity with temperature and the degree of cure was obtained. Predictions of the rate of reaction and the resulting viscosity change by the modified Kamal model and by the empirical model agreed well with the experimental data, respectively, over the temperature range 50–80°C and up to the degree of cure α = 0.4, which are suitable for the mold‐filling stage in the RTM process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2139–2148, 2000     

Ring opening polymerization of ε‐caprolactone initiated by decamolybdate anion: Determination of kinetic and thermodynamic parameters by DSC and 1H‐NMR

The aim of this work is the kinetic and thermodynamic study (by differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (¹H‐NMR)) of the polymerization of ε‐caprolactone initiated by ammonium decamolybdate. By means of isothermal kinetics, enthalpies of reaction in the range 150–160°C, as well as constant rates of polymerization (using an nth‐order kinetics function model), were determined. From an Arrhenius plot, activation energy (E_a = 85.3 kJ/mol) and preexponential factor (A = 1.78 × 10⁸ min^?1) were estimated. Using dynamic methods, crystallization and melting temperatures for the polymer obtained in situ were derived. Kinetic data for polymerization (obtained by ¹H‐NMR) were fitted to 13 different model reaction functions. It was found that power law equations represent better the conversion versus time plots for this system. On the basis of experimental facts, a coordination‐insertion mechanism involving molybdenum(V) species is proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The preparation,characterization, and cure reactions of new bisbenzocyclobutene‐terminated aromatic imides

Several new bisbenzocyclobutene‐terminated aromatic imides, 2,2′‐bis(N‐4‐benzocyclobutenyl) phthalimide, 2,2′‐bis[4‐(N‐4‐benzocyclobutenylphthalimide)]‐ether, 2,2′‐bis[4‐(N‐4‐benzocyclobutenylphthalimide)]‐ketone, and 2,2′‐bis[4‐(N‐4‐benzo cyclobutenylphthalimid‐4‐oxy) phenyl]‐propane, have been synthesized in high yields and characterized by FTIR, MS, EA, and ¹H NMR spectroscopy. The polymers cured from benzocyclobutene‐terminated imides have high glass transition temperature and good thermal stabilities. The cure reaction of an imide was studied by FTIR‐ATR (attenuated total reflection) and DSC techniques. Apparent kinetic parameters of the cure reaction are obtained. The apparent cure reaction order, activation energy, and pre‐exponential factor determined by isothermal DSC method are 1, 143.4 kJ/mol, and 3.88× 10¹³ min^?1, and by nonisothermal DSC methods 1, 139.4 kJ/mol, and 2.27× 10¹³ min^?1, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1705–1719, 2006     

Rheological kinetics of acrylonitrile/amino ethyl‐2‐methyl propenoate copolymer solutions in dimethyl sulfoxide

Viscosity behavior of dimethyl sulfoxide solutions of acrylonitrile (AN)/amino ethyl‐2‐methyl propenoate (AEMP) copolymer was discussed. Rheological kinetics of the solutions was studied in contrast. It is shown that the solutions behave the same as Newtonian flow as the rotor speed goes beyond 12 rpm. With an increase of temperature, the apparent viscosity of AN/AEMP copolymer solutions shows a trend of decrease. The changes of the apparent flow activation energy of solutions calculated by Arrhenius equation become less prominent along with the changes of the molecular weight of AN/AEMP copolymers. The apparent flow activation energy of the copolymer solutions increases continuously with an increase of copolymer concentration. The viscosity of copolymer solutions decreases continuously as the concentrations of KCl and NaCl up to 0.02 mol L^?1, and then it increases. the apparent flow‐activation energy of AN/AEMP copolymer solutions shows an obvious trend of decrease with addition of alkali salts and the changes of the apparent flow‐activation energy of solutions containing NaCl are more prominent than those of solutions containing KCl. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2972–2976, 2006     

Thermal cure of phenylethynyl‐terminated AFR‐PEPA‐4 imide oligomer and a model compound

The thermal cure reactions of phenylethynyl terminated AFR‐PEPA‐4 oligomer and a model compound N‐phenyl‐[4‐(phenylethynyl) phthalimide] were investigated. The kinetics analysis of the thermal cure of AFR‐PEPA‐4 was determined using DSC, with modified DiBenedetto equation. The activation energy of thermal cure reaction of AFR‐PEPA‐4 oligomer is 34.1 kcal/mol with the kinetic order of one, when the reaction conversion is less than 80%. The activation energy of thermal reaction of N‐phenyl‐[4‐(phenylethynyl) phthalimide] is 41.5 kcal/mol with the kinetic order of 0.95. The cure reaction of AFR‐PEPA‐4 imide oligomer can be described as a fast first‐order reaction stage for the formation of polyenes followed by a slow diffusion‐controlled crosslinking reaction stage. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4446–4453, 2006     

One pot synthesis of xanthan gum‐g‐N‐vinyl‐2‐pyrrolidone and study of their metal ion sorption behavior and water swelling property

In this article, graft copolymerization of N‐vinyl‐2‐pyrrolidone onto xanthan gum initiated by potassium peroxydiphosphate/Ag⁺ system in an aqueous medium has been studied under oxygen free nitrogen atmosphere. Grafting ratio, grafting efficiency, and add on increase on increasing the concentration of potassium peroxydiphosphate (2.0 × 10^?3 to 12 × 10^?3 mol dm^?3), Ag⁺(0.4 × 10^?3 to 2.8 × 10^?3 mol dm^?3), and hydrogen ion concentration from 2 × 10^?3 to 14.0 × 10^?3 mol dm^?3. Maximum grafting has been obtained when xanthan gum and monomer concentration were 0.4 g dm^?3 and 16 × 10^?2 mol dm^?3, respectively, at 35°C and 120 min. Water swelling capacity, swelling ratio, metal ion uptake, and metal retention capacity have also been studied, and it has been found that graft copolymer shows enhancement in these properties than pure xanthan gum. The graft copolymer has been characterized by FTIR and thermal analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Grafting of N‐carbamyl maleamic acid onto a styrene–butadiene–styrene copolymer

A styrene–butadiene–styrene block copolymer (SBS) was functionalized with N‐carbamyl maleamic acid (NCMA) using two peroxide initiators with the aim of grafting polar groups onto the molecular chains of the polymer. The influence of the concentration of benzoyl peroxide (BPO) and 2,5‐dimethyl, 2,5‐diterbuthylperoxihexane (DBPH) was studied. The concentration of peroxy groups ranged between 0.75 and 6 × 10^?4 mol % while the concentration of NCMA was constant at 1 wt %. The reaction temperature was chosen according to the type of peroxide employed, being 140°C for BPO and 190°C for DBPH. FTIR spectra confirmed that NCMA was grafted onto the SBS macromolecules. It was found that the highest grafting level was achieved at a concentration of peroxy groups of about 3 × 10^?4 mol %. Contact angle measurements were used to characterize the surface of the SBS and modified polymers. The contact angle of water drops decreased with the amount of NCMA grafted from 95°, the one corresponding to the SBS, to about 73°. T‐peel strength of polymer/polyurethane adhesive/polymer joints made with the modified polymers was larger than those prepared with the original SBS. The peel strength of SBS modified with 1.5 and 3 × 10^?4 mol % of peroxy groups from BPO were five times larger than that of the original SBS. The materials modified using BPO showed peel strengths higher than the ones obtained with DBPH. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4468–4477, 2006     

Poly(L‐lactide). X. Enhanced surface hydrophilicity and chain‐scission mechanisms of poly(L‐lactide) film in enzymatic,alkaline, and phosphate‐buffered solutions

Attempts were carried out to enhance the surface hydrophilicity of poly(L ‐lactide), that is, poly(L ‐lactic acid) (PLLA) film, utilizing enzymatic, alkaline, and autocatalytic hydrolyses in a proteinase K/Tris–HCL buffered solution system (37°C), in a 0.01N NaOH solution (37°C), and in a phosphate‐buffered solution (100°C), respectively. Moreover, its chain‐scission mechanisms in these different media were studied. The advancing contact‐angle (θ_a) value of the amorphous‐made PLLA film decreased monotonically with the hydrolysis time from 100° to 75° and 80° without a significant molecular weight decrease, when enzymatic and alkaline hydrolyses were continued for 60 min and 8 h, respectively. In contrast, a negligible change in the θ_a value was observed for the PLLA films even after the autocatalytic hydrolysis was continured for 16 h, when their bulk M_n decreased from 1.2 × 10⁵ to 2.2 × 10⁴ g mol^?1 or the number of hydrophilic terminal groups per unit weight increased from 1.7 × 10^?5 to 9.1 × 10^?5 mol g^?1. These findings, together with the result of gravimetry, revealed that the enzymatic and alkaline hydrolyses are powerful enough to enhance the practical surface hydrophilicity of the PLLA films because of their surface‐erosion mechanisms and that its practical surface hydrophilicity is controllable by varying the hydrolysis time. Moreover, autocatalytic hydrolysis is inappropriate to enhance the surface hydrophilicity, because of its bulk‐erosion mechanism. Alkaline hydrolysis is the best to enhance the hydrophilicity of the PLLA films without hydrolysis of the film cores, while the enzymatic hydrolysis is appropriate and inappropriate to enhance the surface hydrophilicity of bulky and thin PLLA materials, respectively, because a significant weight loss occurs before saturation of θ_a value. The changes in the weight loss and θ_a values during hydrolysis showed that exo chain scission as well as endo chain scission occurs in the presence of proteinase K, while in the alkaline and phosphate‐buffered solutions, hydrolysis proceeds via endo chain scission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1628–1633, 2003     

Ceric ion‐induced graft copolymerization of acrylamide on cationic guar gum at low temperature

The solution polymerization of acrylamide (AM) on cationic guar gum (CGG) under nitrogen atmosphere using ceric ammonium sulfate (CAS) as the initiator has been realized. The effects of monomer concentration and reaction temperature on grafting conversion, grafting ratio, and grafting efficiency (GE) have been studied. The optimal conditions such as 1.3 mol of AM monomer and 2.2 × 10^?4 mol of CAS have been adopted to produce grafted copolymer (CGG1‐g‐PAM) of high GE of more than 95% at 10°C. The rates of polymerization (R_p) and rates of graft copolymerization (R_g) are enhanced with increase in temperature (<35°C).The R_p is enhanced from 0.43 × 10^?4 mol L^?1 s^?1 for GG‐g‐PAM to 2.53 × 10^?4 mol L^?1 s^?1 for CGG1‐g‐PAM (CGG1, degree of substitute (DS) = 0.007), and R_g from 0.42 × 10^?4 to 2.00 × 10^?4 mol L^?1 s^?1 at 10°C. The apparent activation energy is decreased from 32.27 kJ mol^?1 for GG‐g‐PAM to 8.09 kJ mol^?1 for CGG1‐g‐PAM, which indicates CGG has higher reactivity than unmodified GG ranging from 10 to 50°C. Increase of DS of CGG will lead to slow improvement of the polymerization rates and a hypothetical mechanism is put forward. The grafted copolymer has been characterized by infrared spectroscopy, thermal analysis, and scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3715–3722, 2007     

Study of solution properties of poly(deamino‐tyr‐tyr carbonate hexyl ester) by light scattering and viscometry in dilute and semidilute regime

The structure and properties of poly(deamino‐tyr‐tyr carbonate hexyl ester), in dilute and semidilute solutions, were studied using static, dynamic light scattering, and viscometry. The overlap concentration, c^* is determined by viscosity. The angular dependence of Zimm plots shows no downturn at low angles. In addition, bimodal distribution curves were computed from the quasielastic measurements. The radius of gyration and the second virial coefficient A₂ are found to be respectively 45.8 nm and 9.4 mol cm³ g^?2. The correlation and persistence lengths are discussed. The poly (deamino‐tyr‐tyr carbonate hexyl ester) or poly(DTH‐carbonate) chain in THF, at T = 20°C, behaves as a wormlike chain with persistence length. The persistence length obtained using light scattering is compared with that obtained using viscosity with good agreement. These values obtained from these measurements reflect a high degree of local chain persistence. The reduced viscosity in dilute regime provides a value of apparent viscosity hydrodynamic radius three times lower than obtained by static light scattering. POLYM. ENG. SCI., 50:1605–1612, 2010. © 2010 Society of Plastics Engineers     

Light‐scattering study of poly(hydroxy ester ether) in N,N‐dimethylacetamide solution

Static and dynamic light‐scattering techniques were used to study biodegradable thermoplastic poly(hydroxy ester ether) in N,N‐dimethylacetamide (DMAc). A weight‐average molecular weight M_W = 6.4 × 10⁴ g/mol, radius of gyration R_G = 9.4 nm, second‐virial coefficient A₂ = 1.05 × 10^?3 mol mL/g², translational diffusion coefficient D = 1.34 × 10^?7 cm²/s, and hydrodynamic radius R_H = 8.3 nm are reported. In addition, the effect of H₂O on the polymer chain's conformation and architecture in a DMAc/H₂O solution is evaluated. Results suggest that H₂O makes the mixed solvent poorer as well as promotes polymer chain branching via intramolecular transesterification. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1737–1745, 2001     

Isothermal‐crystallization kinetics and melting behavior of crystalline/crystalline blends of poly(trimethylene terephthalate) and poly(ethylene 2,6‐naphthalate)

The isothermal crystallization and crystal morphology of poly(trimethylene terephthalate) (PTT)/poly (ethylene 2,6‐naphthalate) (PEN) blends were investigated with differential scanning calorimetry and polarized optical microscopy. The commonly used Avrami equation was used to fit the primary stage of isothermal crystallization. The Avrami exponents were evaluated to be in the range of 3.0–3.3 for isothermal crystallization. The subsequent melting endotherms of the blends after isothermal crystallization showed multiple melting peaks. The crystallization activation energies of the blends with 20 or 40% PTT was ?48.3 and ?60.9 kJ/mol, respectively, as calculated by the Arrhenius formula for the isothermal‐crystallization processes. The Hoffman–Lauritzen theory was also employed to fit the process of isothermal crystallization, and the kinetic parameters of the blends with 20 or 40% PTT were determined to be 1.5 × 10⁵ and 1.8 × 10⁵ K², respectively. The spherulite morphology of the six binary blends formed at 190°C showed different sizes and perfect Maltese crosses when the PTT or PEN component was varied, suggesting that the greater the PTT content was, the larger or more perfect the crystallites were that formed in the binary blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3316–3325, 2007     

Copolymers of acrylic acid with 2‐acryloyloxyethyl 2,4‐dichlorophenoxyacetate: Synthesis and herbicide release

Free‐radical copolymerization of acrylic acid with 2‐acryloyloxyethyl 2,4‐dichlorophenoxyacetate using 1.0 mol/L 1,4‐dioxane solution and 1.5 × 10^?2 mol/L of 2,2′ azobisisobutyronitrile as initiator has been carried out at 50°C. In addition to low conversion solution experiments performed to estimate the monomer reactivity ratios, three different copolymerizations over the whole range of conversions have been made. Theoretical values of cumulative copolymer composition, determined by the Mayo‐Lewis terminal model, have been correlated with those experimentally obtained. Finally, the herbicide release in three different aqueous pH buffer solutions has been evaluated in heterogeneous phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4238–4244, 2006     

Synthesis of a star‐shaped poly(ethylene‐co‐propylene) copolymer as a viscosity index improver for lubricants

A saturated star‐shaped poly(ethylene‐co‐propylene) copolymer, (EP)_star, has been synthesized for use as a viscosity index improver in lubricants. Polyisoprene arms were first anionically synthesized using n‐butyllithium as the initiator, followed by a linking reaction with divinylbenzene at the optimum temperature of 60°C. The resulting star‐shaped polyisoprene, (I)_star, was then hydrogenated to eliminate the double bonds of the polyisoprene forming the poly(ethylene‐co‐propylene) structure. The degree of branching (number of arms on each molecule) increases with increase in the mole ratio of divinylbenzene to n‐butyllithium. Increasing the arm length adversely affects the linking efficiency and a minimum amount of tetrahydrofuran (THF) at a THF:n‐butyllithium molar ratio of 1.12 was needed in order to achieve a maximum linking efficiency of approximately 85%. The T_g of poly(ethylene‐co‐propylene) is about 10°C higher than that of the original polyisoprene. Compared with (I)_star, (EP)_star has a thermal decomposition temperature that is 50°C higher but is independent of the arm length or the degree of branching. Viscosity measurement results for (EP)_star reveal that intrinsic viscosity depends only on the arm length but not the degree of branching. Adding 1 wt % of (EP)_star markedly increases the viscosity index of a LN base oil. The addition of 1 wt % of (EP)_star increases the viscosity index (95 for base oil) up to a number between 111 and 145, with the exact number depending upon its arm length and degree of branching. With a fixed arm length, an (EP)_star having a higher degree of branching increases the viscosity index more than one having a lower degree of branching. On the other hand, the viscosity index increases with increase in the arm length when the degree of branching is fixed. Adding 1 wt % of (EP)_star also causes a change in the pour point of the lubricant with the pour point decreasing with increase in the degree of branching. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1911–1918, 2002